The high-definition multimedia interface (HDMI™) is a licensable compact audio/video connector interface for transmitting uncompressed digital streams. The HDMI connects a digital audio/video (or multimedia) source device to a compatible digital audio device and/or a video monitor such as a digital television. In contrast to consumer analog standards, the HDMI enforces digital rights management (DRM) on transmitted media.
Another industrial standard digital multimedia interface is a DisplayPort™ (DP). DisplayPort™ (or DP) is another example for a standard that defines a digital display interface of a digital audio/video interconnect. The DP is intended to be used primarily between a computer and its display monitor, or a computer and a home-theater system.
The Universal Serial Bus (USB) is another connectivity standard primarily utilized to establish communication between devices and a host controller of a PC. However, the USB has also become commonplace on handheld devices, such as mobile phones, smart phones, PDAs, tablet computers, camcorders, and video game consoles. Other interface standards that define the digital display interfaces of a digital audio/video interconnect for handled devices have been recently defined. Examples for such interface standards include the mobile high-definition link (MHL) and Mobility DisplayPort™ (or MyDP).
All of the above connectivity standards provide an interface between a source device and a sink device by proprietary cable and connectors. The source device may be, for example, a set-top box, a DVD player, a personal computer, a video game console, a smart phone, etc., while the sink device may be, for example, a high-definition TV (HDTV). However, different standards can utilize different techniques for interconnecting two circuits, i.e., a line driver and a line receiver. A line driver drives the multimedia signal (Video/Audio) via one of the two coupled circuits, i.e., AC-coupled or DC-coupled. A line receiver is connected in the sink device and is configured to receive multimedia signals.
Specifically, the connectivity of the digital multimedia source is realized through a cable that includes multiple channels. The signals over a channel are transported over a wire or over a pair of differential wires. The cable provides an interconnecting means that is either DC-coupled or AC-coupled.
FIG. 1A illustrates an AC-coupled connectivity between a line driver 110 and a line receiver 120 of source and sink devices respectively. The AC coupling requires placing a coupling capacitor 115 in series with the signal to be coupled. That is, the coupling capacitor 115 connects the source device's line driver 110 and the sink device's line receiver 120. Thus, only AC signals from the source line driver 110 can pass to the sink line receiver 120, while DC signals are blocked.
In contrast, a DC-coupled connectivity, depicted in FIG. 1B, does not require a coupling capacitor to connect the line driver 110 and the line receiver 120 of source and sink devices respectively. The DC signals flow between the multimedia source line driver 110 and sink line receiver 120. The DC levels of such signals, i.e., VH, VL, and VCOMMON-MODE, are set by the supply voltage of source and sink devices.
The AC-coupled connectivity allows, for example, isolating DC bias settings, and is widely used to transmit signals with a zero DC component, known DC-balanced signals. However, in order to reach a DC-balanced signal, a special coding is needed. This special coding requires redundancy bits and hence it increases the baud-rate to be transmitted.
Typically, a line driver (i.e., a line driver 110) is connected via an AC-coupled connectivity or a DC-coupled connectivity, with no ability to select the other coupling option for the same line driver and its data lines. For example, when a line driver is being used with an AC-coupled connectivity, the coupling capacitor 115 cannot be simply bypassed. The different multimedia digital interfaces discussed above utilize different coupling techniques. For example, an HDMI and an MHL are based on a DC-coupled connectivity, while the DisplayPort and USB implement an AC-coupled connectivity.
Therefore, to allow interoperability between different types of multimedia digital interfaces (e.g., HDMI and DisplayPort), there is a need to switch from an AC-coupled to a DC-coupled type of connectivity. One solution to achieve this aim is by means an external cable adaptor. Such an adaptor is typically realized as a dongle which is a repeater connected to the connector. However, an adaptor is an expensive solution in terms of cost and size of its circuits. In addition, the solution of external cable is a fixed solution and cannot dynamically change the type of connectivity. Another solution is to include a switch for bypassing the coupling capacitor 115, when transferring from an AC-coupled to a DC-coupled connectivity mode. However, at high frequency data transfer rates (e.g., Giga hertz rates), such a switch damages the signal integrity. In a multimedia interface, a typical data transfer rate is above 10 Gbps.
Thus, it would be advantageous to have an efficient solution for selecting between coupling connectivity techniques in digital multimedia interfaces.